We propose to investigate the messenger RNA metabolism of differentiating muscle cells in order to determine the kinetics of synthesis and decay of specific, isolated species of messenger RNA. The species of mRNA can then be translated in an in vitro system from wheat germ in order to see if the efficiencies of translation change during the course of development. These in vitro efficiencies can be compared with the cellular efficiencies. The stability of the messengers can be observed during differentiation in order to see if there is any change. Finally, the time of the onset of synthesis of individual messengers can be observed in relation to the differentiation of the cells. BIBLIOGRAPHIC REFERENCES: Spradling, A., Singer, R., Lengyel, J., and Penman, S., 1975, Methods in Cell Biology X, 185-194 (New York, Academic Press). Murphy, R., Singer, R., Saide, J., Blanchard, M., Arnason, M., Young, M., Synthesis and Secretion of Nerve Growth Factor by Muscle Cells in Culture, 1976, Society for Neurosciences (in press).